U.S. patent number 10,710,201 [Application Number 16/076,601] was granted by the patent office on 2020-07-14 for ni-based alloy solid wire for welding and ni-based alloy weld metal.
This patent grant is currently assigned to Kobe Steel, Ltd.. The grantee listed for this patent is Kobe Steel, Ltd.. Invention is credited to Tetsunao Ikeda, Hiroaki Kawamoto, Hiroshi Sugahara.
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United States Patent |
10,710,201 |
Ikeda , et al. |
July 14, 2020 |
Ni-based alloy solid wire for welding and Ni-based alloy weld
metal
Abstract
An Ni-based alloy solid wire for welding has a composition
comprising specific amounts of Cr, Ti, Nb, C, S, Mn and Fe, where
Mo+W, P, Si, Al, Ca, B, Mg, Zr, Co, O, H, and N are controlled to
specific amounts, ([Ti]+[Nb])/[C] is 80 to 150, and the balance is
Ni and inevitable impurities. [Ti], [Nb], and [C] represent the
contents of Ti, Nb, and C (mass %), respectively.
Inventors: |
Ikeda; Tetsunao (Fujisawa,
JP), Sugahara; Hiroshi (Fujisawa, JP),
Kawamoto; Hiroaki (Fujisawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kobe Steel, Ltd. |
Kobe-shi |
N/A |
JP |
|
|
Assignee: |
Kobe Steel, Ltd. (Kobe-shi,
JP)
|
Family
ID: |
59685589 |
Appl.
No.: |
16/076,601 |
Filed: |
February 9, 2017 |
PCT
Filed: |
February 09, 2017 |
PCT No.: |
PCT/JP2017/004808 |
371(c)(1),(2),(4) Date: |
August 08, 2018 |
PCT
Pub. No.: |
WO2017/145783 |
PCT
Pub. Date: |
August 31, 2017 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20190039188 A1 |
Feb 7, 2019 |
|
Foreign Application Priority Data
|
|
|
|
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Feb 22, 2016 [JP] |
|
|
2016-031425 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K
35/0227 (20130101); B23K 35/0261 (20130101); C22C
19/055 (20130101); C22C 19/053 (20130101); B23K
35/304 (20130101); B23K 35/30 (20130101); C22C
19/05 (20130101) |
Current International
Class: |
C22C
19/05 (20060101); B23K 35/02 (20060101); B23K
35/30 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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2002-146497 |
|
May 2002 |
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JP |
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2010-172952 |
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Aug 2010 |
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JP |
|
2011-121088 |
|
Jun 2011 |
|
JP |
|
Other References
English Abstract and English Machine Translation of Sato et al. (JP
2002-146497) (May 22, 2002). cited by examiner.
|
Primary Examiner: Roe; Jessee R
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
The invention claimed is:
1. A Ni-based alloy solid wire for welding, comprising a
composition comprising: Cr: 27.0 to 31.5 mass %, Ti: 0.97 to 2.40
mass %, Nb: 0.30 to 2.40 mass %, C: 0.020 to 0.040 mass %, S:
0.0005 to 0.0030 mass %, Mn: 0.20 to 1.00 mass %, and Fe: 5.0 to
11.0 mass %, and further comprising: Mo+W: 0.5 mass % or less, P:
0.0100 mass % or less, Si: 0.50 mass % or less, Al: 0.20 mass % or
less, Ca: 0.005 mass % or less, B: 0.005 mass % or less, Mg: 0.008
mass % or less, Zr: 0.005 mass % or less, Co: 0.10 mass % or less,
O: 0.015 mass % or less, H: 0.003 mass % or less, N: from 0.015
mass % to greater than 0 mass %, and Ni and inevitable impurities,
wherein ([Ti]+[Nb])/[C] is from 80 to 150, wherein [Ti], [Nb], and
[C] represent the amounts (mass %) of Ti, Nb, and C,
respectively.
2. A Ni-based alloy weld metal produced from by using the Ni-based
alloy solid wire for welding according to claim 1.
3. The Ni-based alloy solid wire of claim 1, wherein the content of
Mg is 0.007 mass % or less.
4. The Ni-based alloy solid wire of claim 1, wherein the contents
of N is from 0.015 mass % to 0.001 mass %.
Description
TECHNICAL FIELD
The present disclosure relates to a solid wire for welding and a
Ni-based alloy weld metal that have a Ni-30Cr-based
composition.
BACKGROUND ART
Ni-based alloys have been used as weld metals for a pressure vessel
and a steam generator in a light-water reactor for nuclear power
generation. Overlay welding with Ni-based alloys have involved
using Ni-15Cr-based or Ni-20Cr-based wire. As a measure against
primary water stress corrosion cracking (PWSCC) generated in weld
metal of Ni-15Cr-based or Ni-20Cr-based wire in pure water, which
is primary cooling water, Ni-30Cr-based wire becomes more widely
used. A weld metal of Ni-30Cr-based wire, however, tends to cause
hot cracking at high temperature during welding compared with that
of Ni-15Cr-based or Ni-20Cr-based wire.
The types of hot cracking include solidification cracking in which
a liquid phase remaining at the final solidification position
before complete solidification of molten weld metal forms openings
due to distortion caused by solidification shrinkage and thermal
shrinkage; liquation cracking in which impurity element-rich
crystal grain boundaries heated to high temperature with welding
heat in a subsequent pass in multilayer welding liquefy and form
openings; and ductility-dip cracking in which grain boundaries
having low cohesive strength in the middle-temperature range not
higher than the solidus temperature form openings in response to
stress acting on the grain boundaries.
A weld metal of Ni-30Cr-based wire has lower tensile strength than
a weld metal of Ni-15Cr-based or Ni-20Cr-based wire. As a result,
the weld metal of Ni-30Cr-based wire has lower tensile strength
than a base metal, and Ni-30Cr-based wire thus imposes a
restriction in device design.
To solve the above-described issues, PTL 1 discloses a Ni-based
alloy solid wire for welding having a composition that contains
specific amounts of Cr, Ti, Nb, Ta, C, and Fe and in which Al, N,
Zr, Mg, P, S, Si, and Mn are controlled to specific amounts or
less, with the balance being Ni and inevitable impurities. PTL 1
describes that the Ni-based alloy solid wire for welding provides
weld metal with the resistance to ductility-dip reheat cracking,
improves the tensile strength of weld metal to larger or equal to
that of a base metal, and offers good welding workability.
PTL 2 discloses a high Cr content Ni-based alloy welding material
having a composition that contains specific amounts of C, Si, Mn,
Cr, Mo, Fe, Cu, Nb+Ta, Al, and Ti and further contains specific
amounts of P and S as inevitable impurities, with the balance being
Ni. PTL 2 describes that the high Cr content Ni-based alloy welding
material can increase tensile strength.
PTL 3 discloses a wire-shaped product formed of a Ni--Cr--Fe alloy
containing specific amounts of Cr, Fe, Mn, Nb+Ta, Mo, Si, Ti, Al,
Cu, Zr, S, B, C, P, and Mg+Ca, with the balance being Ni and
inevitable impurities. PTL 3 describes that the wire-shaped product
can provide desired strength and desired resistance in addition to
the resistance to solidification cracking, ductility-dip cracking,
root cracking, and stress corrosion cracking.
PTL 4 discloses a Ni-based high Cr alloy weld wire having a
composition that contains specific amounts of C, Mn, Fe, Si, Al,
Ti, Cr, Ta, and Mo and further contains specific amounts of Ca+Mg,
N, P, O, S, H, Cu, and Co as inevitable impurities, with the
balance being Ni. PTL 4 describes that the Ni-based high Cr alloy
weld wire can improve the tensile strength of weld zones, the
resistance to weld cracking, the quality of the microstructure of
weld metal, and the welding workability.
CITATION LIST
Patent Literature
PTL 1: Japanese Patent No. 5441870
PTL 2: Japanese Unexamined Patent Application Publication No.
2010-172952
PTL 3: Japanese Patent No. 5420406
PTL 4: Japanese Patent No. 5270043
SUMMARY OF INVENTION
Technical Problem
However, wires known in the art have the following issues: the
effect of avoiding hot cracking is insufficient; and upon post weld
heat treatment (PWHT) for tempering carbon steel after overlay
welding on carbon steel, intermetallic compounds, such as a phase,
precipitate in a region where alloy components, such as Mo, are
concentrated due to solidification segregation, and such
precipitation of alloy components thus makes weld metal brittle.
There is also the following issue: diffusion of carbon from a base
metal toward weld metal in PWHT generates a carburized layer and a
decarburized layer with a bond interposed therebetween and makes
the bond brittle. The term "bond" refers to an interface between a
weld metal and a base metal.
In light of the above-described issues, the present disclosure is
directed to a Ni-based alloy solid wire for welding and a Ni-based
alloy weld metal that are less susceptible to hot cracking, have
high tensile strength, and are unlikely to become brittle even upon
PWHT.
Solution to Problem
A Ni-based alloy solid wire for welding according to a first aspect
of the present invention has a composition that contains Cr: 27.0
to 31.5 mass %, Ti: 0.80 to 2.40 mass %, Nb: 0.30 to 2.40 mass %,
C: 0.020 to 0.040 mass %, S: 0.0005 to 0.0030 mass %, Mn: 0.20 to
1.00 mass %, and Fe: 5.0 to 11.0 mass %, and further contains Mo+W:
0.5 mass % or less, P: 0.0100 mass % or less, Si: 0.50 mass % or
less, Al: 0.20 mass % or less, Ca: 0.005 mass % or less, B: 0.005
mass % or less, Mg: 0.010 mass % or less, Zr: 0.005 mass % or less,
Co: 0.10 mass % or less, O: 0.015 mass % or less, H: 0.003 mass %
or less, and N: 0.015 mass % or less, with the balance being Ni and
inevitable impurities, wherein ([Ti]+[Nb])/[C] is 80 to 150, where
[Ti], [Nb], and [C] represent the amounts (mass %) of Ti, Nb, and
C, respectively.
When the Ni-based alloy solid wire for welding according to the
first aspect of the present invention thus has a composition that
contains specific amounts of Cr, Ti, Nb, C, S, Mn, and Fe and in
which Mo+W, P, Si, Al, Ca, B, Mg, Zr, Co, O, H, and N are
controlled to specific amounts or less, wherein ([Ti]+[Nb])/[C] is
a specific amount (80 to 150), carbides, and carbonitrides, and/or
intermetallic compounds of Ti, Nb, Mo, and W precipitate to improve
the tensile strength of weld metal. When the Ni-based alloy solid
wire for welding according to the first aspect of the present
invention has the above-described composition, precipitation of Ti
and Nb carbides suppresses precipitation of coarse Cr carbide at
grain boundaries, thereby avoiding, for example, intergranular
corrosion and stress corrosion cracking and suppressing an increase
in susceptibility to hot cracking during welding. When the Ni-based
alloy solid wire for welding according to the first aspect of the
present invention has the above-described composition, diffusion of
C from the base metal to the weld metal is unlikely to occur even
after PWHT, suppressing formation of a carburized layer and a
decarburized layer, which have low ductility and low toughness, and
thus suppressing embrittlement of the bond. When the Ni-based alloy
solid wire for welding according to the first aspect of the present
invention has the above-described composition, formation of slags
as a result of adhesion of metal oxides to the weld bead surface is
suppressed to improve welding workability.
A Ni-based alloy weld metal according to a second aspect of the
present invention is produced by using the Ni-based alloy solid
wire for welding.
When the Ni-based alloy solid wire for welding is used for the
Ni-based alloy weld metal according to the second aspect of the
present invention, carbides, and carbonitrides, and/or
intermetallic compounds of Ti, Nb, Mo, and W precipitate to improve
the tensile strength of weld metal. When the Ni-based alloy solid
wire for welding is used for the Ni-based alloy weld metal
according to the second aspect of the present invention,
precipitation of Ti and Nb carbides suppresses precipitation of
coarse Cr carbide at grain boundaries, thereby avoiding, for
example, intergranular corrosion and suppressing an increase in
susceptibility to hot cracking during welding. When the Ni-based
alloy solid wire for welding is used for the Ni-based alloy weld
metal according to the second aspect of the present invention,
diffusion of C from the base metal to the weld metal is unlikely to
occur even after PWHT, suppressing formation of a carburized layer
and a decarburized layer, which have low ductility and low
toughness, and thus suppressing embrittlement of the weld metal.
When the Ni-based alloy solid wire for welding is used for the
Ni-based alloy weld metal according to the embodiment of the
present invention, formation of slags as a result of adhesion of
metal oxides to the weld bead surface is suppressed to improve
welding workability.
Advantageous Effects of Invention
According to the aspects of the present invention, there are
provided the Ni-based alloy solid wire for welding and the Ni-based
alloy weld metal that are less susceptible to hot cracking, have
high tensile strength, and does not become brittle even upon PWHT.
According to the aspects of the present invention, the Ni-based
alloy solid wire for welding and the Ni-based alloy weld metal
offer high corrosion resistance and high welding workability.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram illustrating multilayer overlay
welding.
FIG. 2 is a schematic diagram indicating an all-weld metal test
piece.
DESCRIPTION OF EMBODIMENTS
(First Aspect: Ni-Based Alloy Solid Wire for Wiring)
A Ni-based alloy solid wire for welding according to an embodiment
of the present invention will be described.
The Ni-based alloy solid wire for welding (hereinafter referred to
as a wire) has a composition that contains Cr: 27.0 to 31.5 mass %,
Ti: 0.80 to 2.40 mass %, Nb: 0.30 to 2.40 mass %, C: 0.020 to 0.040
mass %, S: 0.0005 to 0.0030 mass %, Mn: 0.20 to 1.00 mass %, and
Fe: 5.0 to 11.0 mass %, and further contains Mo+W: 0.5 mass % or
less, P: 0.0100 mass % or less, Si: 0.50 mass % or less, Al: 0.20
mass % or less, Ca: 0.005 mass % or less, B: 0.005 mass % or less,
Mg: 0.010 mass % or less, Zr: 0.005 mass % or less, Co: 0.10 mass %
or less, O: 0.015 mass % or less, H: 0.003 mass % or less, and N:
0.015 mass % or less, with the balance being Ni and inevitable
impurities, wherein ([Ti]+[Nb])/[C] is 80 to 150, where [Ti], [Nb],
and [C] represent the amounts (mass %) of Ti, Nb, and C,
respectively.
Effective ways to increase the tensile strength of weld metal
formed by using the wire include solid solution strengthening of a
matrix and strengthening with fine crystallized matter or
precipitates. The presence of Nb, Ti, Mo, and other elements causes
precipitation of carbides and carbonitrides and/or intermetallic
compounds to increase tensile strength. However, a wire containing
these strengthening elements is more susceptible to hot cracking
during welding, and thus there are optimum ranges for the amounts
of strengthening elements.
When a weld metal that is the same type of steel as the base metal
is overlay-welded on carbon steel, which serves as the base metal,
PWHT is typically performed at about 600.degree. C. for the purpose
of tempering the heat-affected zone on the base metal side. It is
thus necessary to ensure the quality and mechanical performance of
the weld zone after PWHT. In PWHT, more carbon diffuses toward the
weld metal from the base metal during PWHT as a difference between
the concentration of C in the weld metal and the concentration of C
in the base metal increases. As a result, a carburized layer with a
high concentration of C is formed on the weld metal side from the
bond, and a decarburized layer with a low high concentration of C
is formed on the base metal side. The carburized layer and the
decarburized layer become thicker as the temperature of PWHT is
higher and the retention time is longer. Since the carburized layer
and the decarburized layer have low ductility and/or low toughness,
there is a risk that application of stress may cause breakage from
these layers. The diffusion of C during the PWHT process is also
affected by the alloy components in the weld metal, and the
presence of Mo and W, which have a great ability to form a carbide,
in the weld metal promotes the diffusion of C, as revealed by
diligent studies. Moreover, excess C that does not combine with Nb
or Ti precipitates at grain boundaries as Cr carbide to degrade
corrosion resistance. Excess Nb and Ti that do not combine with C
precipitate as an intermetallic compound to promote embrittlement
of the weld metal.
The inventors of the present invention found that the formation of
brittle layers adjacent to the bond is avoided by controlling the
amount of Mo and W in the wire but adding C to the wire and
accordingly suppressing the diffusion of C from the base metal to
the weld metal. The precipitation of Cr carbide and intermetallic
compounds is suppressed by controlling ([Ti]+[Nb])/[C] to a
specific amount (80 to 150), which avoids degradation in corrosion
resistance and embrittlement of the weld metal.
The reasons for numerical limitation on the composition of the wire
will be described below.
(Cr: 27.0 to 31.5 Mass %)
Chromium (Cr) is a component indispensable to corrosion resistance
since Cr forms a Cr.sub.2O.sub.3 coating on the surface of the weld
metal and becomes passivated. Therefore, the Cr content is 27.0
mass % or more, and preferably 29.0 mass % or more. The presence of
excess Cr makes it easy to form coarse Cr carbide at grain
boundaries and increases susceptibility to ductility-dip cracking.
Therefore, the Cr content is 31.5 mass % or less, and preferably
31.0 mass % or less.
(Ti: 0.80 to 2.40 Mass %)
Titanium (Ti) is not only dissolved in a Ni matrix but also
precipitated as carbonitride and .gamma.' phase (Ni.sub.3Ti) to
improve the tensile strength of the weld metal. In particular, the
.gamma.' phase forms a fine coherent precipitate in the matrix to
impede dislocation motion; therefore, Ti is a component highly
effective in improving tensile strength. Titanium (Ti) combines
with C to suppress precipitation of Cr carbide at grain boundaries;
therefore, Ti is effective in avoiding intergranular corrosion and
stress corrosion cracking. Moreover, Ti combines with Ni to form
precipitates in grains and at grain boundaries to improve tensile
strength. Therefore, the Ti content is 0.80 mass % or more, and
preferably 0.90 mass % or more. The presence of excess Ti causes
precipitation of a large amount of .gamma.' phase and promotes
embrittlement of the weld metal during PWHT. Excess Ti oxidizes and
surfaces as scale in a molten pool, and the scale adheres to the
weld bead surface to form slag. The molten pool is shielded from
the atmosphere by application of an inert gas during welding, but
the presence of excess Ti hinders complete suppression of slag
formation. Therefore, the Ti content is 2.40 mass % or less, and
preferably 1.80 mass % or less.
(Nb: 0.30 to 2.40 Mass %)
Niobium (Nb) is not only dissolved in the matrix but also forms a
coherent precipitate in the matrix as MC carbonitride and .gamma.''
phase (Ni.sub.3Nb) to improve the tensile strength of the weld
metal. Since the .gamma.'' phase precipitates slower than the
.gamma.' phase, the .gamma.'' phase undergoes a small degree of
embrittlement caused by PWHT. Fine Nb carbide precipitated at grain
boundaries suppresses precipitation of Cr carbides, such as coarse
Cr.sub.23C.sub.6 and Cr.sub.7C.sub.3, at grain boundaries and forms
tortuous grain boundaries through pinning of migrating grain
boundaries to suppress grain boundary sliding, which is effective
in avoiding ductility-dip cracking. Niobium (Nb) combines with C
rather than Cr and thus suppresses intergranular corrosion caused
by precipitation of Cr carbides at grain boundaries. Therefore, the
Nb content is 0.30 mass % or more, and preferably 0.40 mass % or
more.
However, excess Nb tends to be concentrated in dendrite boundaries
due to solidification segregation during solidification of the weld
metal to crystallize or precipitate low-melting-point compounds.
The presence of excess Nb results in generation of solidification
cracking and/or reheat liquation cracking. Excess Nb leads to
noticeable precipitation of the .gamma.'' phase in addition to
carbides and fails to exert the effect of improving corrosion
resistance. Therefore, the Nb content is 2.40 mass % or less, and
preferably 2.20 mass % or less. The same effect is obtained even
when Nb is partially or entirely substituted by Ta, which has
properties similar to those of Nb.
(C: 0.020 to 0.040 Mass %)
Carbon (C) combines with Ti and Nb in the solidification process to
form precipitates at grain boundaries as carbides, such as MC,
M.sub.6C, and M.sub.23C.sub.6, suppressing grain boundary sliding
to avoid ductility-dip cracking and causing precipitation
strengthening to improve tensile strength. When the C content in
overlay weld metal on carbon steel (base metal) is low, carbon (C)
diffuses from the base metal to the weld metal during PWHT, and the
carburized and decarburized layers become thick. This causes, for
example, many fine opening defects adjacent to the bond in the side
bend test. The presence of 0.020 mass % or more of C, preferably
0.025 mass % or more of C, in the wire suppresses the diffusion of
C and prevents generation of defects in the side bend test. For
excess C, an excess of free C not bonded to Ti or Nb combines with
Cr, and Cr carbides such as Cr.sub.23C.sub.6 and Cr.sub.7C.sub.3
precipitate at grain boundaries, forming carbide depletion layers
adjacent to grain boundaries and causing intergranular corrosion
and/or stress corrosion cracking. Therefore, the C content is 0.040
mass % or less, and preferably 0.035 mass % or less.
(S: 0.0005 to 0.0030 Mass %)
Sulfur (S) is segregated and concentrated at grain boundaries
during solidification of weld metal to produce a low-melting-point
compound, and thus causes solidification cracking, reheat liquation
cracking, and/or ductility-dip cracking. Therefore, the S content
is 0.0030 mass % or less, and preferably 0.0018 mass % or less.
However, an excessively low S content results in low wettability of
molten metal and poor dispersion, which causes a deterioration in
weld bead shape. Therefore, the S content is 0.0005 mass % or more,
and preferably 0.0006 mass % or more.
(Mn: 0.20 to 1.00 Mass %)
Manganese (Mn) is used as a deoxidizer in the melting process and
has an effect of improving hot workability by being bonded to
troublesome S. Therefore, the Mn content is 0.20% or more, and
preferably 0.47 mass % or more. In general, the Mn raw material
itself has a high concentration of S. The concentration of S
increases with increasing Mn content, causing hot cracking.
Therefore, the Mn content is 1.00 mass % or less, and preferably
0.60 mass % or less.
(Fe: 5.0 to 11.0 Mass %)
Iron (Fe) is dissolved in the Ni-based alloy to improve hot
workability during wire production. Therefore, the Fe content is
5.0 mass % or more, and preferably 8.2 mass % or more. However,
excess Fe increases the susceptibility to hot cracking during
welding. Therefore, the Fe content is 11.0 mass % or less, and
preferably 9.0 mass % or less.
(Mo+W: 0.5 Mass % or Less)
Molybdenum (Mo) and tungsten (W) improve the tensile strength of
weld metal by way of solid solution strengthening of the matrix and
precipitation of M.sub.6C. The presence of small amounts of Mo and
W provides a weak effect. The presence of large amounts of Mo and W
causes solidification segregation of Mo and W in weld metal and
thus concentration of Mo and W at grain boundaries and/or dendrite
interfaces. For this, the PWHT causes generation of intermetallic
compounds, such as .sigma. phase, and impairs the ductility and
toughness of weld metal. When the overlay weld metal on the base
metal, which is carbon steel, contains Mo and W, carbon (C)
diffuses from the base metal toward the weld metal during the PWHT
process and promotes the formation of carburized and decarburized
layers, causing embrittlement adjacent to the bond and generating
opening defects in the side bend test. Therefore, the total amount
of Mo and W (Mo+W) is 0.5 mass % or less, and preferably 0.3 mass %
or less. The lower limit of Mo+W is preferably 0.1 mass %.
(P: 0.0100 Mass % or Less)
Phosphorus (P) is segregated and concentrated at grain boundaries
during solidification of weld metal to produce a low-melting-point
compound, and thus causes solidification cracking, reheat liquation
cracking, and/or ductility-dip cracking. Therefore, the P content
is 0.0100 mass % or less, and preferably 0.0080 mass % or less.
(Si: 0.50 Mass % or Less)
Silicon (Si) has an effect of improving fluidity of molten metal
but promotes solidification cracking and production of
intermetallic compounds to cause embrittlement. Therefore, Si is
not intentionally added, but the Si content is 0.50 mass % or less,
and preferably 0.22 mass % or less since a commonly available raw
material contains unavoidable Si.
(Al: 0.20 Mass % or Less)
Aluminum (Al) is used as a deoxidizer during melting. Aluminum (Al)
contributes to strengthening by forming a coherent precipitate in
the matrix as the .gamma.' phase in the weld metal and thus
improves tensile strength. In particular, this effect by PWHT is
noticeable. However, when Al is present, the thermal stress
generated by performing PWHT on a welded joint with a high
intensity of restraint causes fine cracks and significantly reduces
toughness. Aluminum (Al) adheres to the weld bead surface as an
oxide to generate slag inclusions. Therefore, the Al content is
0.20 mass % or less, and preferably 0.10 mass % or less. The lower
limit of the Al content is preferably 0.02 mass %.
(Ca: 0.005 Mass % or Less)
Calcium (Ca) adheres to the weld bead surface as an oxide to
generate slag inclusions. Calcium (Ca) makes the arc instable
during MIG welding and causes weld defects. Therefore, the Ca
content includes Ca remaining on the wire surface as a wire drawing
lubricant during wire production. Therefore, the Ca content is
0.005 mass % or less, and preferably 0.002 mass % or less.
(B: 0.005 Mass % or Less, Mg: 0.010 Mass % or Less, and Zr: 0.005
Mass % or Less)
Boron (B), magnesium (Mg), and zirconium (Zr) have an effect of
strengthening grain boundaries by being segregated at grain
boundaries and improving hot workability during wire production.
The presence of excess B, Mg, and Zr causes formation of
low-melting-point compounds at grain boundaries and increases
susceptibility to hot cracking during welding. Magnesium (Mg) and
zirconium (Zr) tend to oxidize and adhere to the weld bead surface
as slags to generate slag inclusions. Therefore, the B content, the
Mg content, and the Zr content are 0.005 mass % or less, 0.010 mass
% or less, and 0.005 mass % or less, respectively, and preferably
0.001 mass % or less, 0.007 mass % or less, and 0.003 mass % or
less, respectively. The lower limit of the Mg content is preferably
0.002 mass %.
(Co: 0.10 Mass % or Less)
Cobalt (Co) contributes to strengthening by being completely
dissolved in Ni, but Co changes into isotope .sup.60Co with a long
half-life upon irradiation with neutrons in a furnace. Thus, Co is
not intentionally added. Therefore, the Co content is 0.10 mass %
or less, and preferably 0.01 mass % or less.
(O: 0.015 Mass % or Less)
Oxygen (O) is contained as a fine oxide base inclusion in the wire.
The oxide base inclusion directly transfers to the weld metal and
is dispersed as it is. When the weld metal is finished with
machining, the inclusion appears as a defect on the processed
surface. Therefore, the O content is 0.015 mass % or less, and
preferably 0.007 mass % or less.
(H: 0.003 Mass % or Less)
Hydrogen (H) in the wire directly transfers to the weld metal and
is segregated mainly at grain boundaries. The segregated H at grain
boundaries weakens the cohesive strength of the grain boundaries
upon tensile deformation of the weld metal, reducing deformation
elongation. Therefore, the H content is 0.003 mass % or less, and
preferably 0.001 mass % or less.
(N: 0.015 Mass % or Less)
Nitrogen (N) generates blowholes in the weld metal. Therefore, the
N content is 0.015 mass % or less, and preferably 0.006 mass % or
less.
(([Ti]+[Nb])/[C]: 80 to 150)
As described above, the wire according to the embodiment of the
present invention contains 0.020 to 0.040 mass % of C. Free C not
bonded to elements such as Ti and Nb in the solidification process
combines with Cr to form precipitates at grain boundaries in PWHT
after overlay welding and to reduce corrosion resistance adjacent
to grain boundaries, causing intergranular corrosion and/or stress
corrosion cracking. Thus, only specifying the absolute values of
the Ti content and the Nb content in the wire is insufficient. For
example, when the C content relative to the total amount of Ti and
Nb is too large, excess C causes Cr carbide precipitation and
degrades corrosion resistance. Therefore, ([Ti]+[Nb])/[C], which is
the ratio of the total amount of Ti and Nb to the C content, is 80
or more and preferably 88 or more. When the C content is too small,
free Ti and free Nb form an intermetallic compound during PWHT to
increase the degree of embrittlement of the weld metal. Therefore,
([Ti]+[Nb])/[C] is 150 or less, and preferably 110 or less.
In this specification, [Ti], [Nb], and [C] represent the amounts
(mass %) of Ti, Nb, and C, respectively.
(Balance)
The balance is Ni and inevitable impurities. The inevitable
impurities are V, Cu, and other elements. Unless the advantageous
effects of the embodiment of the present invention are impaired,
the wire contains V: 0.10 mass % or less and Cu: 0.15 mass % or
less, with the total amount being 0.2 mass % or less. Unless the
amounts of V, Cu, and other elements exceed the above-described
specific amounts, the advantageous effects of the embodiment of the
present invention are not impaired both in the case where V, Cu,
and other elements are contained as inevitable impurities and in
the case where V, Cu, and other elements are added
intentionally.
The elements that are controlled by specifying only the upper
limits as described above, such as (Mo+W), P, Si, Al, Ca, B, Mg,
Zr, Co, O, H, and N, may be contained as inevitable impurities.
(Second Aspect: Ni-Based Alloy Weld Metal)
Next, a Ni-based alloy weld metal according to an embodiment of the
present invention is produced by welding base metals made of steel,
such as carbon steel or stainless steel, using the wire according
to the first aspect of the present invention.
EXAMPLES
Next, Examples of the present invention will be described.
A Ni-alloy ingot was produced through a melting process in a vacuum
melting furnace. The Ni-alloy ingot was then subjected to forging
and rolling and then to wire drawing, whereby a wire having a
diameter of 1.2 mm and the composition shown in Table 1 was
produced.
Using the produced wire, the multilayer overlay welding test was
performed by way of TIG welding. In the multilayer overlay welding
test, as illustrated in FIG. 1, an ASTM A533B steel sheet 50 mm
thick was used as a base metal 1, and a weld metal 2 was formed in
a recess (depth: 15 mm, width of bottom: 85 mm) of the base metal 1
using five-layer overlay welding. The thickness of the weld metal 2
was 15 mm, and the width of the bottom of the weld metal 2 was 85
mm. The all-weld metal test piece illustrated in FIG. 2 was
produced by also using TIG welding. In the all-weld metal test
piece, a weld metal 4 without the influence of dilution of the base
metal was formed by performing buttering welding on the groove face
composed of a backing material 5 and two SM490A steel sheets 13 mm
thick serving as base metals 3. In FIG. 2, the hatched portions
indicate the portions that have undergone buttering welding.
The welding conditions were a welding current of 200 A, an arc
voltage of 11 V, a welding speed of 60 mm/min, a wire feeding speed
of 9 g/min, a shielding gas of 100% Ar, and a shielding gas flow
rate of 15 L/min.
The cracking resistance and corrosion resistance of the weld metal
2 in FIG. 1 were evaluated, and the room-temperature tensile
strength (TS (AW)) and the tensile ductility after PWHT were
evaluated for the weld metal 4 in FIG. 2. The evaluation results
are shown in Table 2.
The evaluation method is as described below.
(Cracking Resistance and Embrittlement of Bond)
Five bend test pieces having a thickness of 10 mm in the direction
perpendicular to the surface of the weld metal 2 were cut out. The
bend test pieces were bent under a condition of a bend radius of
about 50 mm in conformity with JIS Z 2248:2014. The cross section
after bending was subjected to penetrant testing and evaluated for
the number of cracks. The cracking resistance was evaluated as
follows: the number of cracks in five cross sections of the bend
test pieces were counted; and the cracking resistance was rated A
(good) when the average number of cracks per cross section was less
than 5 and there was no defect at the bond, and rated B (poor) when
the average number of cracks per cross section was 5 or more and
there were defects at the bond.
(Room-Temperature Tensile Strength: TS (AW))
One tensile test piece (test piece Al) in conformity with JIS Z
3111:2015 was cut out from the weld metal 4. The tensile test piece
was subjected to tensile strength testing in conformity with JIS Z
3111:2015. The room-temperature tensile strength was rated A (good)
when the average tensile strength was 650 MPa or more, and rated R
(poor) when the average tensile strength was less than 650 MPa.
Note that TS is an acronym for tensile strength and AW is an
acronym for as weld.
(Tensile Ductility after PWHT)
The weld metal 4 was subjected to a heat treatment at 600.degree.
C. corresponding to PWHT. One tensile test piece (test piece A1) in
conformity with JIS Z 3111:2015 was cut out from the weld metal 4
after the heat treatment. The tensile test piece was subjected to
tensile testing in conformity with JIS Z 3111:2015. The tensile
ductility was rated A (good ductility, less embrittlement) when the
average elongation was 35% or more, and rated B (poor ductility,
more embrittlement) when the average elongation was less than
35%.
(Corrosion Resistance)
A test piece was cut out from the weld metal 2 formed by overlay
welding and subjected to corrosion testing in conformity with JIS C
0572:2006. The corrosion resistance was rated A (good) when the
corrosion weight loss was 1.5 g/m.sup.2-hr or less, and rated B
(poor) when the corrosion weight loss was over 1.5
g/m.sup.2-hr.
(Overall Rating)
In overall rating, the case where the cracking resistance, the TS
(AW), the tensile ductility after PWHT, and the corrosion
resistance were all rated A (good) was rated .largecircle.
(acceptable), and the case where at least one of these items was
rated B (poor) was rated x (not acceptable).
The welding workability of multilayer overlay welding was evaluated
by using the following evaluation method. The results are shown in
Table 2.
(Welding Workability)
The amount of slag that adheres to the weld bead surface during
overlay welding was visually observed. The welding workability was
rated A (excellent) when the amount of slag was very small, B
(good) when the amount of slag was small, and C (poor) when the
amount of slag was large.
TABLE-US-00001 TABLE 1 Example/ Comparative Composition of Wire
(mass %, balance: Ni and inevitable impurities) No. Example Cr C Ti
Nb Si Mn P S Mo + W Al Fe Mg A1 Example 29.9 0.033 1.10 2.10 0.22
0.54 0.0060 0.0006 0.2 0.08 9.0 0.007- A2 Example 29.9 0.034 2.00
1.00 0.22 0.52 0.0040 0.0007 0.2 0.10 8.8 0.004- A3 Example 30.2
0.030 1.10 2.20 0.21 0.49 0.0080 0.0018 0.3 0.05 8.2 0.002- A4
Example 29.6 0.031 0.97 2.05 0.20 0.47 0.0020 0.0010 0.1 0.03 8.5
0.004- A5 Example 29.9 0.028 1.91 0.98 0.20 0.48 0.0020 0.0010 0.1
0.02 8.6 0.004- A6 Example 29.3 0.026 1.43 0.98 0.20 0.48 0.0020
0.0010 0.1 0.02 8.5 0.005- A7 Example 29.8 0.027 1.93 0.49 0.20
0.48 0.0020 0.0010 0.1 0.02 8.5 0.004- B1 Comparative 30.0 0.033
1.10 3.40 0.21 0.50 0.0090 0.0013 0.1 0.04 8.5 0- .005 Example B2
Comparative 29.8 0.035 1.10 3.80 0.21 0.53 0.0120 0.0011 0.2 0.06
8.7 0- .003 Example B3 Comparative 29.8 0.030 0.20 2.40 0.21 0.22
0.0080 0.0007 0.2 0.08 8.3 0- .004 Example B4 Comparative 31.2
0.016 0.72 0.54 0.14 0.37 0.0014 0.0004 0.1 0.02 9.2 0- .004
Example B5 Comparative 28.5 0.026 0.83 0.65 0.24 0.55 0.0014 0.0008
0.3 0.02 8.5 0- .003 Example B6 Comparative 30.4 0.021 0.33 0.58
0.21 0.44 0.0028 0.0009 0.2 0.05 8.5 0- .004 Example B7 Comparative
28.1 0.036 0.67 0.54 0.26 0.37 0.0022 0.0009 0.1 0.03 8.6 0- .003
Example B8 Comparative 29.4 0.022 1.89 1.74 0.22 0.55 0.0020 0.0010
0.2 0.04 8.7 0- .003 Example B9 Comparative 30.1 0.023 0.90 0.68
0.28 0.62 0.0018 0.0012 0.1 0.02 9.5 0- .004 Example B10
Comparative 28.9 0.032 1.22 1.45 0.31 0.47 0.0025 0.0014 0.8 0.02
9.1 - 0.002 Example Composition of Wire (mass %, balance: Ni and
inevitable impurities) No. Zr Ca Co N B O H (Ti +Nb)/C A1 <0.005
0.002 0.01 0.003 <0.001 0.005 <0.001 97 A2 <0.005 0.002
0.01 0.004 <0.001 0.006 0.001 88 A3 <0.005 0.001 0.01 0.006
<0.001 0.006 0.001 110 A4 <0.005 <0.001 0.01 0.002
<0.001 0.004 <0.001 97 A5 <0.005 0.001 0.01 0.001
<0.001 0.005 0.001 103 A6 <0.005 0.001 0.01 0.001 <0.001
0.004 <0.001 93 A7 <0.005 0.002 0.01 0.001 <0.001 0.007
0.001 90 B1 <0.005 <0.001 0.04 0.012 <0.001 0.002 0.001
136 B2 <0.005 <0.001 0.05 0.005 <0.001 0.006 <0.001 140
B3 <0.005 <0.001 0.04 0.013 <0.001 0.004 <0.001 87 B4
<0.005 <0.001 0.03 0.007 <0.001 0.004 0.001 79 B5
<0.005 0.001 0.03 0.009 <0.001 0.006 0.001 57 B6 <0.005
0.001 0.04 0.007 <0.001 0.003 0.002 43 B7 <0.005 0.001 0.04
0.013 <0.001 0.006 <0.001 34 B8 <0.005 0.001 0.04 0.006
<0.001 0.005 0.001 165 B9 <0.005 0.001 0.03 0.007 <0.001
0.004 0.002 69 B10 <0.005 0.001 0.04 0.009 <0.001 0.006
<0.001 83 Note: the underlines indicate that the composition
does not satisfy the claims.
TABLE-US-00002 TABLE 2 Tensile Welding Example/ Ductility
Workability Comparative Cracking after Corrosion Overall (amount of
No. Example Resistance TS (AW) PWHT Resistance Rating slag) A1
Example A A A A .largecircle. A A2 Example A A A A .largecircle. B
A3 Example A A A A .largecircle. A A4 Example A A A A .largecircle.
A A5 Example A A A A .largecircle. B A6 Example A A A A
.largecircle. A A7 Example A A A A .largecircle. B B1 Comparative B
A B B X A Example B2 Comparative B A B B X A Example B3 Comparative
B B B B X A Example B4 Comparative B B B B X A Example B5
Comparative A A A B X A Example B6 Comparative B B A B X A Example
B7 Comparative A B A B X A Example B8 Comparative B A B A X B
Example B9 Comparative A A A B X A Example B10 Comparative B A B A
X A Example
As shown in Table 1 and Table 2, Examples (A1 to A7) were rated
.largecircle. (acceptable) because Examples (A1 to A7) satisfy the
composition specified in the claims and thus the cracking
resistance, TS (AW), tensile ductility after PWHT, and corrosion
resistance of Examples (A1 to A7) were all rated A (good). The
welding workability of Examples (A1 to A7) was also rated A
(excellent) or B (good).
Comparative Example (B1) was rated x (not acceptable) because the
Nb content was over the upper limit and thus the cracking
resistance, the tensile ductility after PWHT, and the corrosion
resistance were rated B (poor). Comparative Example (B2) was rated
x (not acceptable) because the Nb content and the P content were
over the upper limits and thus the cracking resistance, the tensile
ductility after PWHT, and the corrosion resistance were rated B
(poor). Comparative Example (B3) was rated x (not acceptable)
because the Ti content was under the lower limit and thus the
cracking resistance, the TS (AW), the tensile ductility after PWHT,
and the corrosion resistance were rated B (poor).
Comparative Example (B4) was rated x (not acceptable) because the C
content, the Ti content, ([Ti]+[Nb])/[C], and the S content were
below the lower limits and thus the cracking resistance, the TS
(AW), the tensile ductility after PWHT, and the corrosion
resistance were rated B (poor). Comparative Example (B5) was rated
x (not acceptable) because ([Ti]+[Nb])/[C] was under the lower
limit and thus the corrosion resistance was rate B (poor).
Comparative Example (B6) was rated x (not acceptable) because the
Ti content and ([Ti]+[Nb])/[C] were below the lower limits and thus
the cracking resistance, the TS (AW), and the corrosion resistance
were rated B (poor). Comparative Example (B7) was rated x (not
acceptable) because the Ti content and ([Ti]+[Nb])/[C] were below
the lower limits and thus the TS (AW) and the corrosion resistance
were rated B (poor).
Comparative Example (BR) was rated x (not acceptable) because
([Ti]+[Nb])/[C] was over the upper limit and thus the cracking
resistance and the tensile ductility after PWHT were rated B
(poor). Comparative Example (B9) was rated x (not acceptable)
because ([Ti]+[Nb])/[C] was under the lower limit and thus the
corrosion resistance was rated B (poor). Comparative Example (B10)
was rated x (not acceptable) because the (Mo+W) content was over
the upper limit and thus the cracking resistance and the tensile
ductility after PWHT were rated B (poor).
The welding workability of Comparative Examples (B1 to B10) was
rated A (excellent) or B (good).
The present application claims priority from Japanese Patent
Application No. 2016-031425 filed Feb. 22, 2016, the entire
contents of which are hereby incorporated by reference.
REFERENCE SIGNS LIST
1, 3 Base metal 2, 4 Weld metal 5 Backing material
* * * * *